Download 3.59 - Poinsettia Fertilization

Alert
by Brian E. Whipker1
([email protected])
Volume 3, Number 59 September 2014
Poinsettia Fertilization:
pH Disorders
Poinsettias are classified
in the general group of
plants as far as optimal pH
is concerned. They respond
well to a pH range of 5.8
to 6.3. Low substrate pH
conditions result in slow
growth. High substrate pH
conditions result in iron
deficiency. This e-GRO
Alert focuses on recognizing pH related symptoms
and management steps to
avoid problems.
Symptoms
So what occurs if the substrate pH becomes too low
or too high?
Department of Horticultural
Science, NC State University
1
2014 Sponsor
© Brian Whipker
Stunting occurs if the substrate pH levels are too low.
Poinsettias respond well to a pH range of 5.8 to 6.3. If
the substrate pH starts to exceed 6.5, then symptoms
of iron deficiency (interveinal chlorosi) develop.
Click to view YouTube summary: Poinsettia pH Disorders
Figure 1. Poinsettias are tolerant of low pH substrate conditions. Plants do
not develop leaf symptoms due to a build up of iron or manganese in the leaf
tissue. Instead, low substrate pH conditions limit the amount of growth and
the plants are stunted (plant on the right).
e-GRO Alert - 2014
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CONTRIBUTORS
Dr. Nora Catlin
Floriculture Specialist
Cornell Cooperative Extension Suffolk County
[email protected]
Dr. Kristin Getter
Floriculture Outreach Specialist
Michigan State University
[email protected]
Dan Gilrein
Entomology Specialist
Cornell Cooperative Extension Suffolk County
[email protected]
Dr. Brian Krug
Floriculture Ext. Specialist
Univ. New Hampshire
[email protected]
Dr. Joyce Latimer
Floriculture Extension & Research
Virginia Tech
[email protected]
Dr. Roberto Lopez
Floriculture Extension Specialist &
Research
Purdue University
[email protected]
Dr. Paul Thomas
Floriculture Extension & Research
University of Georgia
[email protected]
Dr. Brian Whipker
Floriculture Extension & Research
NC State University
[email protected]
Copyright © 2014
Where trade names, proprietary products, or specific equipment
are listed, no discrimination is intended and no endorsement,
guarantee or warranty is implied by the authors, universities
or associations.
In an experiment conducted at NC State University,
we grew Viking poinsettias
at three substrate pH levels. At pH 2.9, the plant
on the right was smaller
and color development was
delayed (Fig. 1). Plants
grown at pH 4.7 and 6.0
were similar in size and
had normal growth. We did
not observe any symptoms
of leaf discoloration, such
as lower leaf bronzing or
black spotting, which one
would expect when other
plants are grown at substrate pHs below 5.0. Slow
growth may be difficult to
observe with poinsettias,
which makes it important
to conduct regular substrate pH tests to ensure
the pH values are within
the optimal range.
the root system. Overwatering or root rot can compromise the roots ability to
take up iron. With severe
iron deficiency symptoms,
the upper foliage ultimately turns completely yellow
(Fig. 4).
Now lets shift to the opposite end of the pH spectrum, elevated values.
Iron deficiency induced by
high substrate pH values
is common with poinsettias. The typical symptom
of iron deficiency is an
interveinal chlorosis (yellowing between the veins)
of the upper leaves (Figs 2
&3). Normally symptoms of
interveinal chlorosis occur
when the pH exceeds 6.5.
Also remember to inspect
Early magnesium deficiency occurs on the lower
foliage. Late season deficiencies that occur after
the bracts have formed
can be confusing because
they also occur in the upper foliage. Usually a full
substrate test and or tissue
test is required to confirm
a magnesium deficiency.
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Keep in mind that the
symptoms of both iron and
magnesium deficiencies
are similar. In both cases
leaves exhibit intervienal
chlorosis. Location of those
symptoms will help you to
diagnose which problem
is occurring. Iron deficiencies occur on the upper,
or younger leaves, while
magnesium deficiency
symptoms occur on the
older leaves. So testing the
substrate to help confirm
your diagnosis.
Management
So what can be done to
prevent problems? If iron
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Cooperating Universities
NC STATE UNIVERSITY
Floriculture
deficiencies occur, first
make sure that the substrate pH is too high by
conducting a substrate
test. If confirmed, the
three iron-type options are
listed in Table 1. Apply the
corrective action, and then
rinse the foliage after application. Retest the substrate pH to confirm that
it is within the acceptable
range between 5.8 and
6.3.
first make sure that the
substrate pH is too low
by conducting a substrate
test. Apply the corrective
action, and then rinse the
foliage after application.
Retest the substrate pH to
confirm that it is within
the acceptable range between 5.8 and 6.3.
Summary
The optimal substrate pH
for poinsettias is between
5.8 and 6.3. Levels below
pH 4.5 result in stunted
If the substrate pH is too
growth and levels above
low, a product such as
6.5 result in high substrate
flowable lime will help
an induced iron deficiency.
increase the pH. A rate of
It is always a good idea to
2 quarts per 100 gallons
conduct a substrate lab
of water will increase the
substrate pH by half a unit. test to confirm pH levels
before making corrective
Repeat the application if
actions.
needed. Before making
a corrective application,
© Brian Whipker
In cooperation with our
local and state greenhouse
organizations
Figure 2. Upper foliage interveinal chlorosis is typical of an iron deficiency induced by elevated substrate pH.
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© Brian
Whipker
© Brian
Whipker
e-GRO Alert - 2014
© Brian Whipker
Figure 3. Close up of the interveinal chlorosis.
Figure 4. Late season problems of iron deficiency can also develop on transition leaves.
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e-GRO Alert - 2014
Table 1. Corrective procedures for overcoming high pH disorders of poinsettias.
Correction Steps – take these steps when
Notes
problems occur
Confirm the substrate pH. Problems generally MISDIAGNOSED OR CONFUSED WITH:
a. Magnesium deficiency results in a similar
occur with the pH is ≥ 6.3.
interveinal chlorosis but of the lower leaves.
b. Iron, manganese or zinc deficiencies – ala. Determine via substrate, fertilizer solution
and tissue analysis if there is a problem of in- though the interveinal chlorosis symptoms are
sufficient Fe being supplied or a problem with similar, these deficiencies occur on the youngest leaves. (Conduct leaf tissue analysis to
waterlogging of the root system.
b. Apply either: (a) 5 oz. iron-EDDHA mixed determine levels.)
c. Virus infection – although the interveinal
in 100 gal. of water (37.4 g in 100 L water);
(b) 5 oz. iron-DTPA mixed in 100 gal. of
chlorosis symptoms are similar, virus sympwater (37.4 g in 100 L water); or (c) 4 to 8 oz. toms most commonly are visible on the
youngest or recently mature leaves. (Conduct
iron sulfate mixed in 100 gal. of water (30 to
60 g in 100 L water). Mist off the foliage soon a virus screening to confirm.)
after application.
In most cases, iron is being supplied in sufc. After making the corrective application,
retest the substrate to determine if the plant is ficient quantities to the soil, but Fe deficiency
can be induced by high pH levels, waterlognow receiving sufficient Fe levels.
ging of the soil, cold soil temperatures, root
injury, or root rot.
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